In an industrial machine with low rigidity, when positioning driving for the industrial machine is performed by a motor, residual vibration sometimes occurs during a stop because of machine resonance or the like. To suppress such residual vibration, a motor control device that actuates the industrial machine via the motor calculates a control signal to reduce a signal component of a vibration frequency (a resonant frequency) of the industrial machine according to a motion target value and performs damping control for the industrial machine. For the motor control device to perform the damping control, a damping parameter for the damping control corresponding to a vibration frequency of a control system including the industrial machine is necessary. For an industrial machine, a vibration frequency of which does not change during motion, if a fixed damping parameter is set in the motor control device, it is possible to sufficiently suppress residual vibration.
On the other hand, among industrial machines, there are industrial machines, vibration frequencies of which change during motion, such as a Cartesian coordinate robot and a crane. For such industrial machines, even if a fixed damping parameter is set in the motor control device, there is a tendency that residual vibration cannot be suppressed.
To solve the problem, Patent Literature 1 describes a machine control device capable of moving an arm in an x-axis direction with a motor for the x-axis and moving a heavy object at an arm distal end in a z-axis direction with a motor for the z-axis. The machine control device changes a parameter (a gain constant) according to a changing vibration frequency of a control target including the arm and the heavy object. Specifically, a data table for control obtains position information concerning a distance from a slide section to the heavy object at the arm distal end and outputs output data related to a correction amount of the vibration frequency. A correction block multiplies a second-order differential value of a position command value with a parameter (a gain constant) obtained from the output data of the data table for control to calculate a correction amount and outputs the correction amount to the adder. The adder adds the correction amount to the original position command. Consequently, according to Patent Literature 1, because the machine control device performs correction taking into account a change in the vibration frequency or the like corresponding to the present position of a part of moving constituent members in the control target, it is possible to stop the control target moved to a predetermined position without vibrating the control target.
Patent Literature 2 describes a control system of a driving device for a crane including a rope engaged with a load to hang the load and a hoisting drum for winding up and winding down the rope. The control system performs feed-forward control to prevent a swing of load from occurring from a signal of rope length. Specifically, the control system detects rope length, sequentially calculates a resonant frequency of the rope from a detection result of the rope length, removes a component of the resonant frequency from a conveyance command limited not to exceed performance of the driving device, and inputs the conveyance command to the driving device for the crane. Consequently, according to Patent Literature 2, it is possible to drive and control the driving device for the crane to prevent the load from greatly swinging at a point when the load is conveyed.